Motor controlling device, compressor, air conditioner and refrigerator

ABSTRACT

A motor controller ( 101 ) according to the invention comprises an inverter circuit ( 3 ) for driving a brushless motor ( 4 ) and a control unit for controlling the rotational speed of the brushless motor ( 4 ) by controlling the phase of the motor current of the brushless motor ( 4 ) through the inverter circuit ( 3 ).

TECHNICAL FIELD

The present invention relates to a motor controller, a compressor andelectric equipment which use the motor controller, and more particularlyrelates to a system for controlling a brushless motor.

BACKGROUND OF THE INVENTION

In recent years, there have been proposed motor controllers which have,at the input side of the inverter circuit, a small-capacity capacitor inplace of a large-capacity smoothing capacitor in view of resource savingand cost reduction.

FIG. 13 is a circuit diagram showing a configuration of such motorcontrollers. In the motor controller shown in FIG. 13 (hereinafterreferred to as the first prior art), since a capacitor 203 is small incapacity, an input voltage to be applied to an inverter circuit 204,which has been obtained by rectifying the output voltage of an a.c.electric power source 201 with a rectifier circuit 202, cannot beensatisfactorily smoothed, so that the input voltage has a pulsatingwaveform. The voltage with such pulsation synchronizes with the outputvoltage of the a.c. power source 201 and has frequency twice that of theoutput voltage of the a.c. power source 201. To cope with this, adesired torque command to be input to a brushless motor 205 is made tohave a waveform which is synchronous with and analogous to the inputvoltage for the inverter circuit 204 as shown in FIG. 14( a). Thereby,the brushless motor 205 can be driven even with a pulsating voltage andthe input current I from the a.c. electric power source 201 has asinusoidal waveform as shown in FIG. 14( b), so that the power factorcan be prevented from decreasing (e.g., Japanese Patent PublicationKokai No. 2002-51589 (FIGS. 1 and 9)).

In the case of brushless motors which drive a compressor used for airconditioners, refrigerators, etc., noise and vibration occur especiallyin a low rotational speed region, owing to great load fluctuation perrotation. Noise and vibration are caused, especially, in rotary-typecompressors and reciprocation-type compressors, for the reason that theload torque imposed on the brushless motor largely fluctuates, as shownin FIG. 15, according to the rotational phase (rotor angle) of the motorto be maximum with the timing at which the refrigerant is discharged sothat the load torque pulsates while the rotor making one rotation. Thepulsation becomes more intense with the average rotational speeddecreasing, and the intense pulsation is accompanied with increases inthe amplitude of vibration. As an attempt to solve this, there has beenproposed a method for controlling motor current so as to reducevibration taking the load fluctuation into account. In this motorcurrent control method (hereinafter referred to as “the second priorart”), acceleration or a change in speed per rotation is computed froman estimated rotational speed of the motor, and a motor current command(amplitude command) is prepared so as to make the change small. Morespecifically, the rotational phase of the motor is divided into desiredsections and, for every divided section, a torque command correctionamount for reducing vibration is prepared from the acceleration or thechange in speed to add to the motor current command. In this motorcurrent control method, since the motor current command largelyincreases or decreases once per rotation of the rotor, the power supplyrate of the a.c. power source also largely increases or decreases eachtime the motor rotates, resulting in a drop in the power factor. Toprevent the power factor from dropping, a high-capacity inductor andhigh-capacity smoothing capacitor are employed (e.g., Japanese PatentPublication Kokai No. 2001-37281 (FIG. 13)).

However, the first prior art has not proved successful in reducing noiseand vibration when applied to a compressor in which a load fluctuationoccurs per rotation, because the torque command varies with frequencytwice the frequency of the power source and the frequency of the loadfluctuation differs from the frequency twice the frequency of the powersource. The second prior also has revealed the problem that if thecapacity of the inductor or smoothing capacitor is simply reduced withthe intention of resource saving or cost reduction, the power factorwill drop, giving adverse effects to the power source system.

DISCLOSURE OF THE INVENTION

The invention is directed to overcoming the foregoing shortcomings and aprimary object of the invention is therefore to provide a motorcontroller and a compressor and electric equipment which employ it, themotor controller being capable of restricting occurrence of vibrationcaused by load torque fluctuations without a drop in the power factoreven if the capacity of the inductor or smoothing capacitor is reduced.

The above object can be accomplished by a motor controller constructedaccording to a first aspect of the invention, the motor controllercomprising:

an inverter circuit for driving a brushless motor; and

a control unit for controlling the rotational speed of the brushlessmotor by controlling the phase of the motor current of the brushlessmotor through the inverter circuit. This arrangement makes it possibleto control the output torque of the brushless motor without causingrotational speed fluctuations, by controlling the phase of the motorcurrent. In this case, the amplitude of the motor current does notchange and it is therefore possible to mitigate vibration caused by loadtorque fluctuations without a drop in the power factor even when ahigh-capacity inductor or high-capacity smoothing capacitor is not used.

The control unit may control the phase of the motor current so as torestrict the rotational speed fluctuation of the brushless motor causedby load torque fluctuation.

The control unit may detect the rotational speed fluctuation androtational phase of the brushless motor based on the rotation of thebrushless motor and may control the phase of the motor current based onthe rotational speed fluctuation and rotational phase which have beendetected.

The control unit may estimate the rotational speed and rotational phaseof the brushless motor based on the motor current of the blushlessmotor, thereby detecting the rotational speed fluctuation and therotational phase. This enables detection of the rotational speedfluctuation and the rotational phase with a simple arrangement.

The control unit may control the phase and amplitude of the motorcurrent of the blushless motor thereby controlling the rotational speedof the blushless motor.

The control unit may control the phase and amplitude of the motorcurrent so as to restrict the rotational speed fluctuation of thebrushless motor caused by load torque fluctuation. This enables it torestrict the rotational speed fluctuation by controlling the phase andamplitude of the motor current in a desired ratio, so that a motorcontroller having a higher degree of freedom can be achieved. Inaddition, the power factor can be set to a desired value.

A rectifier for rectifying an a.c. power output from an a.c. powersource to output to the inverter circuit may be further provided, andthe control unit may control the amplitude of the motor currentaccording to the absolute value of the output voltage of the a.c. powersource. This enables it to control the amplitude of the motor currentsuch that it becomes small during the period when the absolute value ofthe output voltage of the a.c. power source increases and becomes greatduring the period when the absolute value of the output voltage of thea.c. power source decreases, whereby the current output from the a.c.power source can be made smoother and the power factor can be furtherincreased.

A capacitor may be further interposed between d.c. power input terminalsof the inverter circuit. This allows a flow of charging current from thea.c. power source to the capacitor when the output voltage of the a.c.power source connected through the rectifier is higher than the holdvoltage of the capacitor, so that the period of electric conduction canbe prolonged that much and the power factor can be further improved. Inthe case of a motor controller having no smoothing capacitor, vibrationcannot be reduced in spite of controlling the current phase or amplitudeof the motor when high-load operation is performed. In such high-loadoperation, when output torque is small, that is, the motor current issmall, the capacitor is charged to increase the electric current flowingfrom the a.c. power source, so that the output torque becomes large.And, when the motor current is large, the motor current can be increasedby discharging electricity from the capacitor, so that even if thehigh-load operation is carried out, vibration can be restricted withoutcausing a drop in the power factor.

The brushless motor may drive a load the torque of which fluctuates soas to have one peak per rotation of the brushless motor. With thisarrangement, the invention exerts particularly remarkable effects.

According to the invention, there is provided a compressor having thebrushless motor controlled by the motor controller of claim 9 as adriving source.

According to the invention, there is provided an air conditioner havingthe compressor of claim 10 as refrigerant compressing means.

According to the invention, there is provided a refrigerator having thecompressor of claim 10 as refrigerant compressing means.

According to a second aspect of the invention, there is provided a motorcontroller comprising:

a power converter for converting an a.c. power output from an a.c. powersource into a d.c. power;

an inverter circuit for supplying the d.c. power obtained through theconversion by use of the power converter to a brushless motor, therebydriving the brushless motor;

a capacitor connected between d.c. power input terminals of the invertercircuit; and

a control unit for controlling the rotational speed of the brushlessmotor by controlling a motor current of the brushless motor through theinverter circuit,

-   -   wherein the control unit controls the motor current so as to        restrict the rotational speed fluctuation of the brushless motor        caused by load torque fluctuation and controls a current output        from the a.c. power source based on the comparison between the        amplitude of the motor current and the average of the motor        current. With this arrangement, the power factor can be properly        increased by determining whether the motor current is large or        small based on the comparison between the amplitude of the motor        current and the average of the motor current.

The control unit controls a current output from the a.c. power sourcesuch that during the period when the amplitude of the motor current issmaller than the average of the motor current, the capacitor is charged,and during the period when the amplitude of the motor current is largerthan the average, the capacitor discharges electricity. With thisarrangement, a current output from the a.c. power source is controlledaccording to the charge/discharge of the capacitor, so that the powerfactor can be further increased.

The power converter is a rectifier, and a switching element is seriallyconnected to the capacitor between the d.c. power input terminals of theinverter circuit. The control unit controls a current output from thea.c. power source by turning the switching element ON and OFF.

The control unit controls a current output from the a.c. power sourcesuch that during the period when the amplitude of the motor current issmaller than the average of the motor current, the amplitude decreases,and during the period when the amplitude of the motor current is largerthan the average of the motor current, the amplitude increases.

The control unit controls the phase of the motor current so as torestrict the rotational speed fluctuation of the brushless motor causedby load torque fluctuation.

These objects as well as other objects, features and advantages of theinvention will become apparent to those skilled in the art from thefollowing description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a motor controlleraccording to a first embodiment of the invention.

FIG. 2 shows one example of changes in load torque, speed, detectedspeed, detected acceleration and torque command correction amount,relative to the rotor angle of the brushless motor shown in FIG. 1.

FIG. 3 is a block diagram showing a configuration of a fluctuationrestriction unit.

FIG. 4 is a characteristic diagram showing the relationship betweentorque fluctuation and an output current phase command β*.

FIG. 5 is waveform charts when a smoothing capacitor is omitted from asecond prior art, wherein FIG. 5( a) shows a waveform of an a.c. powersource current, FIG. 5( b) shows a waveform of a motor current, and FIG.5( c) shows a waveform of a current amplitude command I*.

FIG. 6 is waveform charts associated with the first embodiment, whereinFIG. 6( a) shows a waveform of an a.c. power source current, FIG. 6( b)shows a waveform of a motor current, and FIG. 6( c) shows a waveform ofa current phase command β*.

FIG. 7 is a block diagram showing a configuration of a motor controlleraccording to a second embodiment of the invention.

FIG. 8 is a block diagram showing a configuration of a motor controlleraccording to a third embodiment of the invention.

FIG. 9 is waveforms associated with the third embodiment of theinvention, wherein FIG. 9( a) shows a waveform of the input voltage ofan inverter circuit and FIG. 9( b) shows a waveform of a currentamplitude command I*.

FIG. 10 is block diagrams showing a configuration of a motor controlleraccording to a fourth embodiment of the invention.

FIG. 11 is a block diagram showing a configuration of a motor controlleraccording to a fifth embodiment of the invention.

FIG. 12 is a block diagram showing a configuration of a motor controlleraccording to a sixth embodiment of the invention.

FIG. 13 is a block diagram showing a configuration of a first prior artmotor controller.

FIG. 14 is a graph showing one example of a torque command for the firstprior art motor controller and one example of the voltage and current ofan a.c. power source.

FIG. 15 is a characteristic diagram showing one example of load torquefluctuation in a conventional rotary-type compressor.

FIG. 16 is a block diagram showing a configuration of a compressoraccording to a seventh embodiment of the invention.

FIG. 17 is a block diagram showing a configuration of an air conditioneraccording to an eighth embodiment of the invention.

FIG. 18 is a block diagram showing a configuration of a refrigeratoraccording to a ninth embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a block diagram showing a configuration of a motor controlleraccording to a first embodiment of the invention.

Turning now to FIG. 1, the motor controller 101 of the first embodimentincludes: a rectifier circuit 2 for rectifying an a.c. power output froma single-phase a.c. power source (hereinafter referred to as “an a.c.power source”) 1; an inverter circuit 3 for converting a d.c. powerobtained by the rectifier circuit 2 into an a.c. power to supply to abrushless motor 4; and a current sensor 102 for detecting a current(hereinafter referred to as “a motor current”) flowing in the blushlessmotor 4; and a control unit 5 for drivingly controlling the invertercircuit 3 based on the motor current detected by the current sensor 102.Herein, the brushless motor 4 drives, for instance, a compressor (notshown).

Herein, the rectifier 2 consists of a full-wave rectifier and theinverter circuit 3 consists of a voltage-type inverter.

The control unit 5 consists of a computing unit such as a micro-computerand includes a rotational speed/rotational phase estimation unit 6, afluctuation restriction unit 7, a rotational speed error detection unit8, a current command preparation unit 9 and an applied voltagepreparation unit 10.

The rotational speed/rotational phase estimation unit 6 estimates therotational phase and rotational speed of the brushless motor 4 based onthe motor current detected by the current sensor 102 and outputs them asan estimated rotational speed ω^ and an estimated rotational phase θ.Herein, the current sensor 102 detects a current flowing in athree-phase coil of the brushless motor 4. The estimation of therotational phase and rotational speed may be done by use of a voltagevalue applied to the brushless motor 4, a motor constant indicative of acharacteristic of the brushless motor 4, etc. Alternatively, theestimation may utilize the conventional technique commonly used inposition-sensorless sinusoidal driving of a blushless motor. In the caseof a motor controller for driving a brushless motor having a positionsensor, the rotational phase and rotational speed may be obtained basedon a signal from the position sensor. In this case, the need for therotational speed/rotational phase estimation unit 6 is obviated.

The fluctuation restriction unit 7 computes the rotational speedfluctuation of the brushless motor 4 caused by load torque fluctuationbased on the estimated rotational speed ω^ output from the rotationalspeed/rotational phase estimation unit 6 and outputs a current phasecommand β* to the current command preparation unit 9 to restrict therotational speed fluctuation of the brushless motor 4.

The rotational speed error detection unit 8 prepares a current amplitudecommand I* from an error corresponding to the difference between arotational speed command ω* input from the outside of the motorcontroller 101 and the estimated rotational speed ω^ output from therotational speed/rotational phase estimation unit 6 to output to thecurrent command preparation unit 9.

The current command preparation unit 9 prepares a d-axis current commandI_(d)* and a q-axis current command I_(q)* from the current amplitudecommand I* and current phase command β* which have been input, using thefollowing Equation (2) and output them to the applied voltagepreparation unit 10. As seen from Equation (2), the current phasecommand β* is indicative of the phase difference between the q-axis andmotor current vector when the voltage and current supplied to the motorare plotted on a d/q coordinate system.I _(d) *=I*×sin(β*), I _(q) *=I*×cos(β*)  (2)

The applied voltage preparation unit 10 detects a d-axis current valueI_(d) and a q-axis current value I_(q) from the motor current valuedetected by the current sensor 102 and the estimated rotational phase θoutput from the rotational speed/rotational phase estimation unit 6, andprepares a value of voltage to be applied to the brushless motor 4 suchthat the d-axis current value I_(d) and the q-axis current value I_(q)become equal to the d-axis current command I_(d)* and the q-axis currentcommand I_(q)*. Then, the applied voltage preparation unit 10 outputsthis voltage value to the inverter circuit 3 as a PWM signal. That is,feed-back control is performed such that the d-axis current value I_(d)becomes equal to the d-axis current command I_(d)* and the q-axiscurrent value I_(q) becomes equal to the q-axis current command I_(q)*.As such feed-back control, the PI control generally known may be used oralternatively, other control methods than the PI control may be used.Since the input voltage of the inverter circuit 3 largely pulsates whenpreparing a value of voltage to be applied to the brushless motor 4, theinput voltage of the inverter circuit 3 may be detected to correct thePWM signal (the PWM signal is not shown).

The inverter circuit 3 turns each switching element ON and OFF based onthe PWM signal which has been input, thereby applying the voltagedetermined by the applied voltage preparation unit 10 to the brushlessmotor 4.

The series of operations described above is continuously effected inevery control cycle, whereby the motor current of the brushless motor 4has a desired current amplitude and current phase. As used herein, “thedesired current amplitude and current phase” refer to such currentamplitude and current phase that make the rotational speed of thebrushless motor 4 comply with the rotational speed command ω* andrestrict the rotational speed fluctuation.

The configuration and principle of the fluctuation restriction unit 7which features the invention will be explained by way of a concreteexample.

FIG. 2 shows one example of changes in load torque, speed, detectedspeed, detected acceleration and torque command correction amount,relative to the rotor angle of the brushless motor shown in FIG. 1. FIG.3 is a block diagram showing a configuration of the fluctuationrestriction unit 7.

First, the configuration of the fluctuation restriction unit 7 will bedescribed.

Turning to FIG. 3, the fluctuation restriction unit 7 has (i) a rotoracceleration detection unit 11 for detecting the acceleration(hereinafter referred to as “detected acceleration”) of the rotor basedon the estimated rotational speed ω^ input from the rotationalspeed/rotational phase estimation unit 6 (see FIG. 1); (ii) a subtracter12 for calculating the deviation (herein referred to as “accelerationerror”) of a detected acceleration from a target acceleration (0); (iii)first to n-th acceleration control units Ac1 to Acn for calculating,based on the acceleration error computed by the subtracter 12, thetorque command correction amount for each of N intervals (hereinafterreferred to as “rotor angle intervals”) into which the angle of therotor when the rotor makes one rotation is divided; (iv) a current phasecommand conversion unit 14 for converting each torque command correctionamount into a current phase command correction amount; and (v) a currentphase command correction amount interpolation unit 15 for preparing acurrent phase command β* through linear interpolation of the currentphase command correction amounts.

Next, the principle of the fluctuation restriction unit 7 will beexplained.

In FIGS. 1 to 3, the load torque fluctuates largely according to theangle of the rotor as discussed earlier in the description of the priorart, especially in the case of rotary-type and reciprocation-typecompressors. If such load torque fluctuations are present, therotational speed (hereinafter referred to as “speed”) of the rotor ofthe brushless motor 4 fluctuates such that it decreases as the loadtorque increases and increases as the load torque decreases, as shown inFIG. 2. On the other hand, the acceleration of the rotor (hereinafterreferred to as “acceleration”) fluctuates in an opposite manner to theload torque, that is, the acceleration decreases as the load torqueincreases. Since it is required that the vibration of the compressor bereduced, the output torque of the brushless motor 4 is maximized with arotor angle which provides a great load torque and the output torque ofthe brushless motor 4 is reduced when the load torque is at a smalllevel, whereby the torque can be well balanced, thereby mitigatingvibration. To this end, the speed fluctuation should be reduced. It isclear that speed fluctuation can be reduced by controlling the torque soas to make the acceleration component zero. Therefore, the acceleration(i.e., detected acceleration) is firstly computed (detected) bycalculating a change in the value of the input estimated rotationalspeed ω^ by the rotor acceleration detection unit 11. Then, anacceleration error is obtained from the deviation of the accelerationfrom the target acceleration 0 by the subtracter 12. Since the torquefluctuation has a certain pattern with respect to the rotational phase,control free from the influence of control delays can be performed bychanging control conditions according to the rotational phase.

Specifically, when controlling the acceleration of the rotor, unlesscontrol is performed on the acceleration corresponding to a specifiedrotational phase, the control performance gets worse owing to controldelays occurring in the acceleration control. To cope with this, theangle of the rotor when it makes one rotation is divided into aplurality of intervals (N intervals) and arithmetic operation foracceleration control is effected for every interval. This arithmeticoperation is performed with the following Equation (1).tr(n+1, i)=tr(n,i)−Ga×a(i)  (1)

where

tr (n, i): inverter torque command (n=the number of rotations, i=rotorangle interval)

a (i): acceleration (i=rotor angle interval)

Ga: control gain

Herein, the angle of the rotor is divided into N rotor angle intervalsand, in the first to n-th acceleration control units Ac1 to Acn, thearithmetic operation for acceleration control is performed for everyrotor angle interval. As a result, each of the first to n-thacceleration control units Ac1 to Acn outputs a torque commandcorrection amount for its corresponding rotor angle interval. Since therotor angle interval to be controlled changes as the rotor rotates, itis necessary to switch the acceleration control unit which operatescorrespondingly to the present rotor angle interval, selecting from theunits Ac1 to Acn. This switching operation is carried out based on theestimated rotational phase θ input from the rotational speed/rotationalphase estimation unit 6. This torque command correction amount functionsto keep the rotational speed of the brushless motor 4 constant. Further,this torque command correction amount is converted into a current phasecorrection amount by the current phase command conversion unit 14. Ifthe phase of the motor current is advanced, the generated torque (outputtorque) of the brushless motor 4 decreases. Conversely, if the phase ofthe motor current is retarded, the generated torque of the brushlessmotor 4 increases. Thus, when the torque command correction amount islarge, the current phase correction amount to be output is small andwhen the torque command correction amount is small, the current phasecorrection amount is large. In addition, it is more desirable to put alimit on this current phase correction amount. For instance, in caseswhere the brushless motor 4 is a salient polar motor, the phase of themotor current which allows the output torque of the motor to be maximumis present at a certain rotor angle between 0 degree and 90 degrees.With the phases of the motor current smaller and larger than thiscertain rotor angle, torque decreases. Therefore, the current phasecorrection amount is limited such that the phase of the rotor fallswithin the range of from the certain rotor angle to 90 degrees. If thebrushless motor 4 is a non-salient polar motor, the phase of the motorcurrent which provides the maximum output torque is 0 degree. Therefore,the current phase correction amount is limited so as to make the phaseof the motor current fall within the range of from 0 degree to 90degrees.

In addition, since the actual rotor angle is continuous, N current phasecorrection amounts are interpolated according to the rotor angle by thecurrent phase command correction amount interpolation unit 15 and thevalue obtained from the interpolation is output as a final current phasecommand β*. As this rotor angle, the estimated rotational phase θ inputfrom the rotational speed/rotational phase estimation unit 6 is used.

FIG. 4 is a characteristic diagram showing the relationship betweentorque fluctuation and the output current phase command β*.

Turning to FIGS. 1 to 4, the first to n-th acceleration control unitsAc1 to Acn output N current phase correction amounts per rotation. The Ncurrent phase correction amounts are interpolated by the current phasecommand correction amount interpolation unit 15 and the value obtainedfrom the interpolation is output as a current phase command β*.

As this interpolation, the linear interpolation is employed herein.

As shown in FIG. 4, the current phase command β* varies relative to therotor angle such that it becomes smaller as the load torque is greaterand it becomes greater as the load torque is smaller. Roughly speaking,the current phase command β* varies so as to have a phase substantiallyopposite to that of the load torque. Thereby, the output torque of thebrushless motor 4 varies relative to the rotor angle, correspondingly tofluctuations in the load torque.

Next, there will be explained a driving circuit for the brushless motorand the operation of the motor controller.

FIG. 5 is waveform charts when a smoothing capacitor is omitted from thesecond prior art, wherein FIG. 5( a) shows a waveform of an a.c. powersource current, FIG. 5( b) shows a waveform of a motor current, and FIG.5( c) shows a waveform of the current amplitude command I*. FIG. 6 iswaveform charts associated with the first embodiment, wherein FIG. 6( a)shows a waveform of an a.c. power source current, FIG. 6( b) shows awaveform of a motor current, and FIG. 6( c) shows a waveform of thecurrent phase command β*.

In FIGS. 1 to 4, an a.c. voltage output from the a.c. power source 1 isrectified by the rectifier circuit 2 to produce a pulsating d.c. voltagewhich is, in turn, supplied to the inverter circuit 3. FIG. 9( a) showsone example (a full-wave rectified waveform) of the pulsating d.c.voltage. The inverter circuit 3 converts the pulsating d.c. power intoan a.c. power and applies a voltage determined by the control unit 5 tothe brushless motor 4, thereby driving the brushless motor 4. At thattime, the load torque of the brushless motor 4 fluctuates so as to haveone peak per rotation of the rotor as shown in FIG. 4. Based on themotor current of the brushless motor 4 detected by the current sensor102, the control unit 5 prepares the current phase command β* whichvaries in a sinusoidal pattern as shown in FIG. 6( c) and has a phasesubstantially opposite to the phase of the load torque. The control unit5 drivingly controls the inverter circuit 3 based on this current phasecommand β*. Thereby, the phase of the motor current of the brushlessmotor 4 varies as shown in FIG. 6( b) as the rotor rotates, so that theoutput torque of the brushless motor 4 corresponds to the fluctuation ofthe load torque. As a result, the vibration caused by the speedfluctuation which the load fluctuation entails can be reduced. Since theamplitude of the motor current at that time is constant as shown in FIG.6( b), the amplitude of the current output from the a.c. power source 1does not vary as seen from FIG. 6( a) even if a motor controller havingno high-capacity smoothing capacitor is used (the motor controller ofthe present embodiment does not use a smoothing capacitor itself) and,in consequence, the power factor does not drop. Accordingly, thevibration prevention control does not adversely affect the businessdistribution line system.

In contrast with this, in the case where the second prior art from whichthe smoothing capacitor is eliminated is applied to a compressor, theamplitude of the motor current varies as shown in FIG. 5( b), andaccording to this, the amplitude of the current output from the a.c.power source 1 varies as shown in FIG. 5( a), resulting in a drop in thepower factor. Therefore, it adversely affects the business distributionline system.

As described above, the first embodiment enables it to mitigatevibration attributable to the load torque fluctuation without causing adrop in the power factor and without adversely affecting the businessdistribution line system.

While the above description has been presented in terms of a case wherethe load torque fluctuates with a peak per rotation of the rotor, theinvention is equally applicable to cases where the load torque varies inother arbitrary patterns.

While the current phase command is prepared based on acceleration by thefluctuation restriction unit 7 in the above description, it is readilyapparent that the same effect could be attained with preparation of thecurrent phase command based on, for instance, speed.

While the inverter circuit 3 is constituted by a voltage-type inverterin the above description, it could be constituted by a current-typeinverter.

Second Embodiment

FIG. 7 is a block diagram showing a configuration of a motor controllerconstructed according to a second embodiment of the invention. In FIG.7, corresponding or identical parts are once again indicated with thesame reference numerals as in FIG. 1. In the second embodiment, thecontrol unit 5 has an adder 16 as shown in FIG. 7. The fluctuationrestriction unit 7 further outputs a current amplitude correctioncommand I_(h)*. The adder 16 adds the output of the rotational speederror detection unit 8 to the current amplitude correction commandI_(h)* to output to the current command preparation unit 9. In terms ofother features, the second embodiment does not differ from the firstembodiment.

For speed fluctuation control, the fluctuation restriction unit 7prepares the current phase command β* and the current amplitude commandcorrection value I_(h)* based on, for example, the estimated rotationalspeed ω^ and estimated rotational phase θ which have been input. Thetorque correction amount may be obtained in the same way as in the firstembodiment, and based on the result, the current phase command β* andthe current amplitude command correction value I_(h)* are determined. Asexplained earlier in the first embodiment, for reducing the outputtorque of the blushless motor 4 (hereinafter referred to as “outputtorque”), the current phase command β* may be increased or the currentamplitude value may be reduced. For increasing the output torque, thecurrent phase command β* may be reduced or the current amplitude valuemay be increased. It is free to decide which way will be chosen. Therange of the current amplitude command correction value I_(h)* may beset in compliance with the desired value of the power factor. Forinstance, if the desired value of the power factor is 0.9 or more, it isadvisable to set the current amplitude command correction value I_(h)*such that the maximum/minimum ratio of the current amplitude command I*during the period when the rotor makes one rotation becomes about 0.3 ormore. If the desired value of the power factor is 0.95 or more, it isadvisable to set the current amplitude command correction value I_(h)*such that the maximum/minimum ratio of the current amplitude command I*becomes about 0.5 or more. Thus, the possible range of the currentamplitude command correction value I_(h)* is set according to thedesired value of the power factor and the current amplitude command I*is determined. If the vibration control in this condition turns out tobe unsatisfactory, vibration can be restricted by increasing or reducingthe current phase command β*.

As described above, the second embodiment can provide a motor controllerhaving a higher degree of freedom, because the fluctuation restrictionunit 7 releases the current amplitude command correction value I_(h)*and the current phase command β* which restrict speed fluctuations. Inaddition, the second embodiment can provide a motor controller operablewith a desired power factor.

Third Embodiment

FIG. 8 is a block diagram showing a configuration of a motor controlleraccording to a third embodiment of the invention. FIG. 9 is waveformsassociated with the third embodiment, wherein FIG. 9( a) shows awaveform of the input voltage of an inverter circuit and FIG. 9( b)shows a waveform of the current amplitude command I*. In FIG. 8, theparts corresponding to or identical with those of FIG. 1 are identifiedby the same reference numerals.

In the third embodiment, the motor controller 101 further includes avoltage sensor 103 for detecting the output voltage of the a.c. powersource 1, and the control unit 5 further includes an amplitudemodulation unit 17 for modulating the output of the rotational speedfluctuation detection unit 8 based on the phase of the voltage detectedby the voltage sensor 103 to output to the current command preparationunit 9 as the current amplitude command I*. In terms of other features,the third embodiment does not differ from the first embodiment.

Concretely, the voltage (input voltage) to be applied to the invertercircuit 3 pulsates as shown in FIG. 9 (a). The input voltage of theinverter circuit 3 fluctuates according to changes in the absolute valueof the output voltage of the a.c. power source 1. When the absolutevalue of the output voltage is great, the input voltage of the invertercircuit 3 is high and therefore a current easily flows in the brushlessmotor 4. In cases where a small-capacity capacitor (not shown) is placedbetween the inverter circuit 3 and the rectifier circuit 2, a chargecurrent for the capacitor is generated when the output voltage of thea.c. power source (more precisely, the rectifier circuit 2) becomeshigher than the voltage of the capacitor.

The amplitude modulation unit 17 is designed to modulate the output ofthe rotational speed fluctuation detection unit 8 based on the voltagephase of the a.c. power source detected by the voltage sensor 103 inorder to prepare the current amplitude command I* with which, as shownin FIG. 9( b), the current flowing in the brushless motor 4 becomessmall during the period when the absolute value of the output voltage ofthe a.c. power source 1 increases and becomes great during the periodwhen the absolute value of the output voltage of the a.c. power source 1drops. The amplitude modulation unit 17 outputs the command I* to thecurrent command preparation unit 9. As a result, the fluctuatingfrequency of the current amplitude command I* becomes twice thefrequency of the a.c. power source 1.

By virtue of this arrangement, the current flowing from the a.c. powersource 1 becomes smoother, resulting in an improved power factor.Although the third embodiment has been discussed in terms of a casewhere the first embodiment is modified, the second embodiment may besimilarly modified. In this case, the output of the amplitude modulationunit 17 shown in FIG. 8 may be input to the adder 16 shown in FIG. 2.

Fourth Embodiment

FIG. 10( a) is a block diagram showing a configuration of a motorcontroller constructed according to a fourth embodiment of theinvention. In FIG. 10( a), the parts corresponding to or identical withthose of FIG. 1 are identified by the same reference numerals.

In the fourth embodiment, the motor controller 101 further includes acharging/discharging circuit 18 disposed between the rectifier circuit 2and the inverter circuit 3.

The charging/discharging circuit 18 is constituted by a capacitorconnected between the output terminals of the rectifier circuit 2.

With this arrangement, if the output voltage of the rectifier circuit 2exceeds the voltage held by the capacitor, charging of the capacitorstarts. This charging is constantly done when the pulsating outputvoltage of the rectifier circuit 2 is higher than the voltage held bythe capacitor. When the output voltage of the rectifier circuit 2 islower, the capacitor is discharged. If the motor controller 101 does nothave the charging/discharging circuit 18, the minimum of the inputvoltage of the inverter circuit 3 becomes approximately 0 V as shown inFIG. 9 (a). Therefore, the capacitor of the charging/discharging circuit18 is completely discharged in synchronization with the output voltageof the a.c. power source 1 at a frequency which is one-half of thefrequency of the output voltage. Since discharging is invariably carriedout at a frequency that is one-half of the output voltage of the a.c.power source 1, whenever the output voltage of the a.c. power source ishigh, a current for charging flows so that the flow rate of current fromthe a.c. power source 1 increases. As a result, the period of electricconduction prolongs, leading to an improved power factor. In addition,vibration can be mitigated without causing a drop in the power factoreven when high-load operation is carried out. Further, the electriccapacitance C[F] of the capacitor of the charging/discharging circuit 18may be higher than 0[F] and no more than 2×10⁻⁷×P[F] where the powerconsumption of the brushless motor 4 is represented by P[W].

Although the fourth embodiment has been discussed in terms of a casewhere the first embodiment is modified, it is readily apparent that thesame effect can be attained by similar modification of the second orthird embodiment.

The charging/discharging circuit 18 may be replaced with acharging/discharging circuit 18 a composed of a Zener diode and acapacitor which are interconnected in series as shown in FIG. 10( b).This arrangement does not differ from the charging/discharging circuitshown in FIG. 10( a) except that charging of the capacitor starts whenthe output voltage of the rectifier circuit 2 exceeds the sum of thevoltage held by the capacitor and the yield voltage of the Zener diode.In this arrangement, current flows in the same manner as described aboveand the effect of improving the power factor can be achieved like theabove-described case. If it is desired that the incoming current (thefirst current flowing at an instant charging of the capacitor isstarted) flowing into the Zener diode be reduced, a resistor (not shown)may be serially connected in addition to the Zener diode and thecapacitor. The electric capacitance of the capacitor of thecharging/discharging circuit 18 a may be approximately the same as thatof the charging/discharging circuit 18.

Obviously, provision of an inductor inserted between the a.c. powersource 1 and the rectifier circuit 2 will bring about a further improvedpower factor that the higher harmonic component of the current isrestricted (not shown). The inductance L[H] of this inductor may be morethan 0[H] and no more than 9×10⁻⁹×C[H], where the electric capacitanceof the capacitor is represented by C[F].

Fifth Embodiment

FIG. 11 is a block diagram showing a configuration of a motor controlleraccording to a fifth embodiment of the invention. In FIG. 11, the partscorresponding to or identical with those of FIG. 1 are identified by thesame reference numerals.

The motor controller 101 of the fifth embodiment further includes acharging/discharging circuit control unit 19, a charging/dischargingcircuit 20, the voltage sensor 103 and a current sensor 104. With regardto other features, the fifth embodiment does not differ from the firstembodiment.

The charging/discharging circuit 20 is composed of a two-way switch anda capacitor which arc interconnected in series between the outputterminals of the rectifier circuit 2. The two-way switch serves as acharging switch and discharging switch. The charging/discharging circuitcontrol unit 19 includes a torque command on/off determination unit 21,an a.c. current command preparation unit 22, a charging switch commandpreparation unit 23 and a discharging switch command preparation unit24.

The torque command on/off determination unit 21 determines in responseto the current amplitude command I* from the control unit 5 whether ornot the current amplitude command value to be given to the brushlessmotor 4 is large or small. The way of determination is such that theaverage of the current amplitude commands I* issued when the rotor makesone rotation (hereinafter referred to as “the average current amplitudecommand value”) is obtained and it is then determined whether thepresent current amplitude command I* (hereinafter referred to as “thepresent current amplitude command value”) is larger or smaller than theaverage current amplitude command value. The result of the determinationis output to the a.c. current command preparation unit 22.

The a.c. current command preparation unit 22 detects the voltage phaseof the a.c. power source 1 through the voltage sensor 103 and preparesan a.c current command Iac* based on the result of the determinationmade by the torque command on/off determination unit 21. During theperiod that it is judged in the above determination that the presentcurrent amplitude command value is smaller than the average currentamplitude command value (hereinafter referred to as “the period 1”), thea.c. current command Iac* is prepared based on the voltage phase of thea.c. power source 1. During the period that the present currentamplitude command value is determined to be larger than the averagecurrent amplitude command value (hereinafter referred to as “the period2”), outputting of the a.c. current command Iac* is stopped. During theperiod 1, since the value of the voltage applied to the brushless motor4 by the inverter circuit 3 is small, the motor current is small.Therefore, most of the current incoming from the a.c. power source 1(hereinafter referred to as “a.c. power source current”) is used forcharging the capacitor of the charging/discharging circuit 20.

The a.c. current command Iac* is prepared so as to limit the amplitudevalue of the a.c. power source current such that the voltage of thecapacitor does not become overvoltage in the period 1. The a.c. currentcommand Iac* thus prepared is input to the charging switch commandpreparation unit 23. The charging switch command preparation unit 23performs feedback control to make the value of the a.c. power sourcecurrent detected by the current sensor 104 equal to the a.c. currentcommand Iac*. The feedback control is carried out through the PWMoperation of the charging switch of the charging/discharging circuit 20.Although the PI control is generally utilized for the feedback algorithmused herein, the feedback algorithm is not limited to this.

During the period 2, the a.c. current command Iac* is not input to thecharging switch command preparation unit 23 and therefore the chargingswitch is stopped.

During the period 2, the value of the voltage applied to the brushlessmotor 4 by the inverter circuit 3 is large so that the motor current islarge. Therefore, the a.c. power source current is large. However, whenthe output voltage of the a.c. power source 1 is low, it becomesdifficult to apply a desired voltage to the brushless motor 4. To solvethis problem, the discharging switch command preparation unit 24 turnsthe discharging switch of the charging/discharging circuit 20 ON,thereby applying a desired voltage to the brushless motor 4 and, at thesame time, allowing the capacitor to be charged during the next period1. The discharging switch command preparation unit 24 determines atiming for turning the discharging switch ON, based on the voltage phaseof the a.c. power source 1 detected by the voltage sensor 103.

The operation described above is continuously performed whenever thebrushless motor 4 makes one rotation, so that the power factor of thea.c. power source 1 can be increased.

It should be noted that the control unit 5 may be constituted by thecontrol unit of the second prior art which restricts vibration bycontrolling the amplitude of the motor current.

Sixth Embodiment

FIG. 12 is a block diagram showing a configuration of a motor controlleraccording to a sixth embodiment of the invention. In FIG. 12, the partscorresponding to or identical with those of FIG. 11 are identified bythe same reference numerals.

In the sixth embodiment, there are provided a converter circuit 25 and aconverter circuit control unit 26, as shown in FIG. 12, in place of thecharging/discharging circuit 20 and charging/discharging circuit controlunit 21 of the fifth embodiment (FIG. 11). The motor controller of thesixth embodiment further includes a voltage sensor 105. Except the abovepoints, the sixth embodiment does not differ from the fifth embodiment.

The converter circuit 25 consists of a known circuit having an inductor,a switching element, a diode and a capacitor.

The converter circuit control unit 26 has the torque command on/offdetermination unit 21, the a.c. current command preparation unit 22, anda charging/discharging command preparation unit 29.

The torque command on/off determination unit 21 is the same as that ofthe fifth embodiment. An a.c. current command preparation unit 28detects the voltage phase of the a.c. power source 1 through the voltagesensor 103 and prepares a sinusoidal a.c. current command. Thecharging/discharging command preparation unit 29 detects the a.c. powersource current through the current sensor 104 and feedback controls thea.c. power source current such that it meets the a.c. current command.This feedback control is carried out in such a way that thecharging/discharging command preparation unit 29 outputs a PWM controlsignal to the switching element of the converter circuit 25 and theswitching element is switched according to the PWM signal. Although thePI control is generally employed as the feedback control, the feedbackcontrol is not limited to this.

The a.c. current command preparation unit 28 prepares a.c. currentcommands having different amplitude values depending on the period 1 andthe period 2. In the period 1, since the motor current of the brushlessmotor 4 is made small, little current flows into the inverter circuit 3.Therefore, the capacitor of the converter circuit 25 is charged withcurrent based on the a.c. current command. On the other hand, in theperiod 2, current flows into the brushless motor 4 by way of theinverter circuit 3, so that power is supplied from the a.c. power source1 at the same time that the charged capacitor is discharged. Therefore,the amplitude value of the a.c. current command is reduced in the period1, whereas the amplitude value of the a.c. current command is increasedin the period 2. It should be noted that the ratio of the amplitudevalue of the a.c. current command in the period 2 to the amplitude valuein the period 1 may be set to 0.3 or more if the desirable power factoris 0.9 and set to 0.5 or more if the desirable power factor is 0.95.However, it is necessary to make the charging amount and dischargingamount of the capacitor when the brushless motor 4 rotates once equal toeach other, and therefore the a.c. current command preparation unit 22detects the hold voltage of the capacitor through the voltage sensor 105and adjusts the amplitude value of the a.c. current command based on it.

Seventh Embodiment

According to a seventh embodiment of the invention, there will beexplained a compressor to which the motor controller of any of the firstto sixth embodiments is applied.

FIG. 16 is a block diagram showing a configuration of a compressor 41according to the seventh embodiment of the invention.

In FIG. 16, the compressor 41 connected to the a.c. power source 1 hasthe motor controller 101 and a compression mechanism 42 driven by thebrushless motor 4. The brushless motor 4 and a.c. power source 1 of theseventh embodiment are configured and function similarly to those of thefirst embodiment. The motor controller 101 consists of the motorcontroller of any of the first to sixth embodiments described earlier.The output of the motor controller 101 is input to the brushless motor 4disposed in the compression mechanism 42 and the brushless motor 4 isrotatively driven by the motor controller 101. The rotation of thebrushless motor 4 allows the compression mechanism 42 to compress asuctioned refrigerant and discharge it as a high-pressure refrigerant.

The compression mechanism 42 is a rotary type or reciprocation typemechanism and imparts load fluctuations to the brushless motor 4, theload fluctuations being synchronous with the rotation of the brushlessmotor 4. By use of the motor controller of any of the first to sixthembodiments, the speed fluctuation of the brushless motor 4 isrestricted so that a compressor having less vibration and a high powerfactor can be achieved. In addition, since a high-capacity inductor andcapacitor are eliminated, the invention can provide a compact,light-weight compressor.

Eighth Embodiment

According to an eighth embodiment of the invention, there will beexplained an air conditioner to which the motor controller of any of thefirst to sixth embodiments is applied.

FIG. 17 is a block diagram showing a configuration of an air conditioner43 according to the eighth embodiment of the invention.

In FIG. 17, the air conditioner 43 of the eighth embodiment has anindoor unit 44 and outdoor unit 45 by which cooling (and heating) of theroom is carried out. The outdoor unit 45 has the compressor 41 whichconsists of the compressor of the seventh embodiment having thecompression mechanism 42 and the motor controller 101. The motorcontroller 101 is connected to the a.c. power source 1. As describedearlier, the compression mechanism 42 is driven by a brushless motor(not shown in FIG. 17) disposed therein and the brushless motor iscontrolled by the motor controller 101. The brushless motor and the a.c.power source 1 are configured and function similarly to those of thefirst embodiment. The motor controller 101 consists of the motorcontroller of any of the first to sixth embodiments.

The compression mechanism 42 allows the refrigerant to circulate betweenthe indoor unit 44 and the outdoor unit 45.

The indoor unit 44 has an indoor heat exchanger 48 interposed in acirculation path for the refrigerant (hereinafter referred to as“refrigerant circulation path”). The indoor heat exchanger 48 includes afan 48 a for increasing the heat exchange ability of the indoor heatexchanger 48 and a temperature sensor 48 b for measuring the temperatureof the indoor heat exchanger 48 or its ambient temperature.

The outdoor unit 45 has, in addition to the compressor 41, a four-wayvalve 46 interposed in the refrigerant circulation path, a throttlesystem 47, and an outdoor heat exchanger 49. The outdoor heat exchanger49 includes a fan 49 a for increasing the heat exchange ability of theindoor heat exchanger 49 and a temperature sensor 49 b for measuring thetemperature of the indoor heat exchanger 49 or its ambient temperature.

The four-way valve 46 is switched to connect the outlet port and inletport of the compression mechanism 42 to the refrigerant circulationpath. By switching the four-way valve 46, the flowing direction of therefrigerant within the refrigerant circulation path can be changed. Forinstance, if the flowing direction of the refrigerant which flows in therefrigerant circulation path of the air conditioner 43 is switched tothe direction indicated by arrow A, the refrigerant which has passedthrough the outdoor heat exchanger 49 is suctioned by the compressionmechanism 42 through the four-way valve 46, and the refrigerantdischarged from the compression mechanism 42 is fed to the indoor heatexchanger 48. On the other hand, if the flowing direction of therefrigerant is changed to the direction indicated by arrow B byswitching the four-way valve 46, the refrigerant which has passedthrough the indoor heat exchanger 48 is suctioned by the compressionmechanism 42 through the four-way valve 46, and the refrigerantdischarged from the compression mechanism 42 is fed to the outdoor heatexchanger 49. Thus, the flowing direction of the refrigerant is changedby switching the four-way valve 46.

The throttle system 47, which is disposed in the refrigerant circulationpath for interconnecting the indoor heat exchanger 48 and the outdoorheat exchanger 49, has both the throttling function of reducing the flowrate of the circulating refrigerant and the valve function ofautomatically adjusting the flow rate of the refrigerant. While therefrigerant is circulating in the refrigerant circulation path, thethrottle system 47 reduces the flow rate of the liquid refrigerant sentfrom the condenser to the evaporator to expand the liquid refrigerantimmediately thereafter, and at the same time, supplies the evaporatorwith a necessary amount of refrigerant that is neither too much nor toolittle. In this air conditioner 43, the indoor heat exchanger 48 servesas a condenser in heating operation and as an evaporator in coolingoperation. In the condenser, the high-temperature, high-pressure gaseousrefrigerant flowing therein is gradually liquefied as it is deprived ofheat by air sent in, so that it is brought into a high-pressure liquidstate or a liquid-gas mixed state, in the neighborhood of the outlet ofthe condenser. This is equal to the liquefaction of the refrigerantaccompanied with heat dissipation to the atmosphere. The refrigerant inthe liquid state or the liquid-gas mixed state, which has come to havelow temperature and lower pressure in the throttle system 47, flows intothe evaporator. If surrounding air is sent into the evaporator in thiscondition, the refrigerant deprives the air of a lot of heat andevaporates to include increased gas. The air, which has been deprived ofa lot of heat in the evaporator, is released through the nozzle of theindoor unit 44 or outdoor unit 45 in the form of cold blasts.

In the air conditioner 43, a rotational speed command for the brushlessmotor is set based on driving conditions, that is, a target temperatureset for the air conditioner 43, actual room temperature and outdoor airtemperature. As discussed earlier in the first embodiment, the motorcontroller 101 controls the rotational speed of the brushless motor ofthe compression mechanism 42 based on the set rotational speed command.

Next, the cooling and heating operations of the air conditioner 43 ofthe above-described configuration will be explained.

Turning to FIG. 17, the air conditioner 43 is formed such that when adriving voltage from the motor controller 101 is applied to thebrushless motor (not shown) of the compression mechanism 42, therefrigerant circulates within the refrigerant circulation path. At thattime, heat exchanging is carried out by the heat exchanger 48 of theinside unit 44 and the heat exchanger 49 of the outside unit 45.Specifically, a known heat pump cycle is established in the closedcirculation path for the refrigerant by allowing the refrigerantconfined in the refrigerant circulation path to circulate by thecompression mechanism 42. Thereby, the inside of the room is heated orcooled.

When heating is performed by the air conditioner 43 for instance, thefour-way valve 46 is set through operation by the user such that therefrigerant flows in the direction indicated by arrow A. In this case,the indoor heat exchanger 48 operates as a condenser and heat isdissipated through refrigerant circulation in the refrigerantcirculation path. Thereby, the inside of the room is heated.

On the other hand, when cooling is performed by the air conditioner 43,the four-way valve 46 is set through operation by the user such that therefrigerant flows in the direction indicated by arrow B. In this case,the indoor heat exchanger 48 operates as an evaporator and the heat ofsurrounding air is taken in through refrigerant circulation in therefrigerant circulation path. Thereby, the inside of the room is cooled.

During operation, in the air conditioner 43, a rotational speed commandis determined based on a target temperature set for the air conditioner43, actual room temperature and outdoor air temperature, and therotational speed of the brushless motor of the compression mechanism 42is controlled by the motor controller 101 based on the determinedrotational speed command as described earlier in the first embodiment.As a result, the air conditioner 43 performs cooling or heating to makethe room comfortable.

The above discussion has been presented in terms of an air conditionercapable of both cooling and heating. Where the invention is applied toan air conditioner for cooling only, the four-way valve 46 may beeliminated and the refrigerant may be made to flow in the directionindicated by arrow B.

As described above, the invention can provide an air conditioner using acompressor which does not use a high-capacity inductor nor capacitor.

Ninth Embodiment

FIG. 18 is a block diagram showing a configuration of a refrigeratoraccording to a ninth embodiment of the invention.

A refrigerator 51 according to the ninth embodiment has the compressor41, a condenser 52, a chillroom evaporator 53 and a throttle system 54.The compressor 41 consists of the compressor of the seventh embodimentincluding the compression mechanism 42 and the motor controller 101.Connected to the motor controller 101 is the a.c. power source(single-phase a.c. power source) 1. As described earlier, thecompression mechanism 42 is driven by a brushless motor (not shown inFIG. 18) disposed therein and this brushless motor is controlled by themotor controller 101. The brushless motor and the a.c. power source 1are configured and function similarly to those of the first embodiment.The motor controller 101 consists of any one of the motor controllersdescribed in the first to sixth embodiments. The compression mechanism42 allows circulation of the refrigerant. In the circulation path forthe refrigerant, the condenser 52, the throttle system 54 and thechillroom evaporator 53 are arranged in this order in the circulatingdirection of the refrigerant.

The condenser 52 condenses the high-temperature, high-pressure gaseousrefrigerant flowing therein to emit the heat of the refrigerant to theair. The refrigerant gas sent into the condenser 52 is graduallyliquefied when deprived of heat by the air, so that it gets into ahigh-pressure liquid state or a liquid-gas mixed state in theneighborhood of the outlet of the condenser 52.

Like the throttle system 47 of the air conditioner 43 according to theeighth embodiment, the throttle system 54 expands the refrigerant byreducing the flow rate of the refrigerant sent from the condenser 52while the refrigerant circulating in the refrigerant circulation path,and, at the same time, supplies the chillroom evaporator 53 with anecessary amount of refrigerant that is neither too much nor too little.

The chillroom evaporator 53 evaporates the low-temperature refrigerantthereby cooling the inside of the refrigerator. The chillroom evaporator53 includes a fan 53 a for increasing the efficiency of heat exchangeand a temperature sensor 53 b for detecting the inside temperature ofthe refrigerator.

Next, there will be explained the operation of the refrigerator 51having the structure described above.

Turning to FIG. 18, in the refrigerator 51, after the motor controller101 applies a driving voltage to the brushless motor (not shown) of thecompression mechanism 42, the compression mechanism 42 is put inoperation so that the refrigerant circulates in the direction indicatedby arrow within the refrigerant circulation path. At that time, thecondenser 52 and the chillroom evaporator 53 perform heat exchange,thereby cooling the inside of the refrigerator 51. In other words, therefrigerant, which has been condensed by the condenser 52, is expandedwith its flow rate being reduced by the throttle system 54 and becomes alow-temperature refrigerant. After sent to the chillroom evaporator 53,the low-temperature refrigerant evaporates within the chillroomevaporator 53, thereby cooling the inside of the refrigerator. At thattime, the fan 53 a forcibly sends air existing within the refrigeratorto the chillroom evaporator 53 so that the chillroom evaporator 53 canperform efficient heat exchange.

In the refrigerator 51, a rotational speed command is set according to atarget temperature for the refrigerator 51 and the inside temperature ofthe refrigerator, and, based on this set rotational speed command, themotor controller 101 controls the rotational speed of the brushlessmotor of the compression mechanism 42 similarly to the eighthembodiment. As a result, the inside of the refrigerator 51 is maintainedat the target temperature.

Since the refrigerator 51 of the ninth embodiment has the compressor 41which causes less vibration and has a low power factor, the degree offreedom for the position of the motor controller 101 within therefrigerator 51 increases compared to the conventional motorcontrollers. Thanks to the increased degree of freedom of thearrangement of the motor controller 101, the capacity of therefrigerator 51 increases. In addition, since the refrigerator 51 hasthe light-weight motor controller 101, the weight of the refrigerator 51can be reduced.

Numerous modifications and alternative embodiments of the invention willbe apparent to those skilled in the art in view of the foregoingdescription. Accordingly, the description is to be construed asillustrative only, and is provided for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Thedetails of the structure and/or function maybe varied substantiallywithout departing from the spirit of the invention and all modificationswhich come within the scope of the appended claims are reserved.

INDUSTRIAL APPLICABILITY

The motor controller of the invention is well suited for use incompressors etc.

The compressor of the invention is well suited for use in electricequipment such as air conditioners and refrigerators.

The air conditioner of the invention is capable of restricting vibrationgenerated by load torque fluctuations without causing a drop in thepower factor.

The refrigerator of the invention is capable of restricting vibrationgenerated by load torque fluctuations without causing a drop in thepower factor.

1. A motor controller comprising: an inverter circuit for driving abrushless motor; a control unit for detecting rotational speedfluctuation of a brushless motor caused by load torque fluctuation andcontrolling a phase and an amplitude of a motor current of the brushlessmotor so as to restrict said rotational speed fluctuation via theinverter circuit; and a rectifier for rectifying an a.c. power outputfrom an a.c. power source to output to the inverter circuit, wherein thecontrol unit controls the amplitude of the motor current according to anabsolute value of an output voltage of the a.c. power source such that acurrent flowing in the brushless motor becomes small during a periodwhen the absolute value of the output voltage of the a.c. power sourceincreases and becomes great during a period when the absolute value ofthe output voltage of the a.c. power source decreases.
 2. The motorcontroller according to claim 1, further comprising a capacitorinterposed between d.c. power input terminals of the inverter circuit.3. The motor controller according to claim 1, wherein the brushlessmotor drives a load the torque of which fluctuates so as to have onepeak per rotation of the brushless motor.
 4. A compressor having thebrushless motor controlled by the motor controller of claim 3, as adriving source.
 5. An air conditioner having the compressor of claim 4,as refrigerant compressing means.
 6. A refrigerator having thecompressor of claim 4, as refrigerant compressing means.
 7. A motorcontroller comprising: a power converter for converting an a.c. poweroutput from an a.c. power source into a d.c. power; an inverter circuitfor supplying the d.c. power obtained through the conversion by use ofthe power converter to a brushless motor, thereby driving the brushlessmotor; a capacitor connected between d.c. power input terminals of theinverter circuit; and a control unit for controlling the rotationalspeed of the brushless motor by controlling the motor current of thebrushless motor, wherein the control unit controls the motor current viathe inverter circuit so as to restrict the rotational speed fluctuationof the brushless motor caused by load torque fluctuation and controls acurrent output from the a.c. power source to the power converter basedon the comparison between the amplitude of the motor current and theaverage of the motor current.
 8. The motor controller according to claim7, wherein the control unit controls the current output from the a.c.power source such that during the period when the amplitude of the motorcurrent is smaller than the average of the motor current, the capacitoris charged, and during the period when the amplitude of the motorcurrent is larger than the average, the capacitor dischargeselectricity.
 9. The motor controller according to claim 8, wherein thepower converter is a rectifier, wherein a switching element is seriallyconnected to the capacitor between the d.c. power input terminals of theinverter circuit, and wherein the control unit controls the currentoutput from the a.c. power source by turning the switching element ONand OFF.
 10. The motor controller according to claim 8, wherein thecontrol unit controls the current output from the a.c. power source suchthat during the period when the amplitude of the motor current issmaller than the average of the motor current, said amplitude decreases,and during the period when the amplitude of the motor current is largerthan the average of the motor current, said amplitude increases.
 11. Themotor controller according to claim 7, wherein the control unit controlsthe phase of the motor current so as to restrict the rotational speedfluctuation of the brushless motor caused by load torque fluctuation.